Collector electrode for electrostatic precipitator

ABSTRACT

A collector electrode for an electrostatic precipitator is provided in strips having spaced apart beads extending transversely to a rapping or jolting bar, the strips being symmetrically about a median transverse plane and having edges profiled with trapezoidal cross-section and legs co-operating with the legs of adjacent or contiguous strips to define labyrinth seals.

United States Patent 11 1 1111 3,755,991 Steuernagel 1 Sept. 4, 1973 1541 COLLECTOR ELECTRODE FOR 2,946,400 7/1960 Gustafsson 55/130 ELECTROSTATIC PRECIPITATOR 3,282,029 1l/l966 Steuemagel 55/141 3,418,792 12/1968 Quintilian et al.. 55/156 [75] Inventor: Walter Steuernagel, Frankfurt am 3 435 594 4 1969 Steuemagel 55 1 12 Main, Germany 3,660,968 5/1972 Dyla et a1. 55/130 .[73] Assignee: Metallgesellschaft Aktiengesellschaft, FOREIGN PATENTS OR APPLICATIONS Frankfurt am Main, Germany 859,870 1/1961 Great Britain 1. 55 130 922,543 4/1963 Great Britain'..... [22] June 1971 966,558 8/1964 Great Britain 55 154 [21] Appl. No.: 154,086

Primary ExaminerDennis E. Talbert, Jr. [30] Foreign Application Priority Data AttOmey Karl Ross '20 970 G G 70 23 234.7 June 1 many 57 ABSTRACT [52] US. Cl 55/112, 55/130, 55/156 A Collector e ec ode for an electrostatic precipitator [51] Int. Cl. B03c 3/76 i provi in s rips having spaced apart beads extend- [58] Field of Search 55/112, 130, 154, ing transversely to a rapping or jolting the Strips 55/156 being symmetrically about a median transverse plane and having edges profiled with trapezoidal cross- [5 6] Ref ren es Cited section and legs co-operating with the legs of adjacent UNITED STATES PATENTS or contiguous strips to define labyrinth seals.' 2,812,035 11/1957 Sohlman et a1. 55/112 3 Claims, 4 Drawing Figures PATENTED SEP 4 93 Attorney COLLECTOR ELECTRODE FOR ELECTROSTATIC PRECIPITATOR l. FIELD OF THE INVENTION The present invention relates to an electrostatic .precipitator and, more particularly, to collector-electrode arrangements for electrostatic precipitators.

2. BACKGROUND OF THE INVENTION In general, an electrostatic precipitato rcomprises an electrode system including corona-discharge electrodes and collector electrodes, means for inducing a gas flow through the precipitator and along the electrode system, means for removing precipitated particles, etc. The corona discharge generated at the discharge electrodes ionizes a gas stream containing particles which generally cannot be removed efficiently by filtering, sedimentation and like methods, the particles picking up electric charge from the ions of the gas stream. The particles are attracted to, and tend to accumulate upon, the collector electrodes to which they adhere by electrostatic forces. It is a common practice to remove the adherent deposit by jolting or rapping the collector electrodes, thereby causing the particles to be dislodged by the collector electrodes and to fall into a bin or the like for collection of the solids. The same principles apply, of course, to electrostatic separators and other systems for removing or recovering particulate matter from a gas stream. Sometimes, the electrostatic precipitator follows or is downstream of a mechanical separator in which particles of larger size are recovered.

In modern electrostatic precipitators, having collector surfaces of a total area of 15,000 to 30,000 square meters, any improvements in the shape of the electrodes, and simplification of manufacture and installation may be significant in reducing the costs involved in construction, maintenance and repair of existing installations and the capital cost of new gas-purifying systems.

It has been proposed to provide collector electrodes To stiffen the collector electrodes and prevent such membranous damping of the rapping or vibrational energy, the collector electrodes are provided with a profiled configuration, i.e., are deformed to have channels, crests, corrugations or beads which stiffen the otherwise flat central portion. High vibratability and minimum damping of a collector electrode strip is not, however, sufficient to insure high-collecting power or efficiency because the rapping of the electrode may result in the formation of a dust cloud or agitation of the dust such that part of the dust may be entrained with the gas to reduce the efficacyof the system. It has been proposed, to avoid or reduce this problem, to provide socalled low-flow zones in the channels traversed by the gas between the collector plates and in which the velocity of the gas drops. Such low-flow zones are able to preventdynamic entrainment of the dust particles or to produce the necessary reduction of the velocity of the collector electrodes presenting surfaces upon which the particles (generally dust) are deposited.

To remove the dust which has been deposited on the collector electrodes, the latter are rapped or jolted, as previously noted, and may be provided with a rapping rod along the bottoms of the electrodes.

For efficient removal of dust from the collector electrodes,.the latter must be strips which are stiff and easily vibratable so that the vibrational energy applied by the rap is distributed throughout the collector electrode with minimum damping. The problem of vibrational damping, of course, derives from the fact that a thin sheet-metal member, engaged at two edges, constitutes a membrane capable of internal deformation. To the extent that the rapping energy is converted into such membranous deformation, the force is lost as a dust-shedding energy.

gas for sedimentation of any particles which may have been entrained. The low-flow zones may be formed by chambers produced by deformation of the sheet-metal electrodes and constitute dust-receiving chambers to facilitate removal of the dust. The profile of the electrodes from such chambers, of course, further stiffens the electrode strips.

Adjacent collector-electrode strips are often locked together in tight hook joints as may be made, for example, in thesheet-metal art, by clamping two hook portions in interfitting relationship together, may be joined by welding or rivetting or may be connected in some other rigid manner so that the resulting collector electrode array is continuous in the sense that no openings are provided therein and the array is as stiff as possible.

A close spacing of the collector electrodes, as described above, has the disadvantage that a strictly straight or aligned arrangement of the electrodes cannot be made in practice because any deviation in dimensions of the electrodes from one another will result in bends and distortion of the array. Manufacturing tolerances for collector electrode strips must be made high in spite of the fact that these strips may have lengths of about 12 meters, thereby considerably adding to the cost of production. In spite of attempts to make hook-type joints as tight as possible, in spite of welding or rivetting of the joints, and in spite of conventional efforts known to applicant to prevent transverse movement of gas from a channel on one side of a collector plate to a channel on the other, such transverse flow appears to occur through gaps between the strips which cannot be avoided at low cost. The transverse flow advantageously affects dust collection, may

cause dispersion or reentrainment of the dust after a rap or jolt has been administered, etc.

3. OBJECTS OF THE INVENTION It is also an object of the invention to provide an improvedelectrostatic precipitator.

4. SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter, are attained, in accordance with the present invention, with a strip-shaped collector electrode, i.e., a collector electrode of sheetmetal having a thickness of l to 1.5 mm and a height in excess of its width, which has a generally flat or planar central portion and trapezoidal longitudinal edge portions, i.e., edge portions unitarily and integrally deformed and profiled along the length'of the strip to have a trapezoidal crosssection and at least one free leg forming part of the trapezoid. The leg is formed with an outwardly bent flange or foot so that, when the collector strips are deposited in substantially contiguous relationship, i.e., side by side in a common plane, the legs of adjoining trapezoids reach toward the other and forman overlap with an air gap between them. The air gap thus constitutes a labyrinth seal. The longitudinal edge portions of the collector electrodes thus define low-flow trapezoidal receiving chambers through which the collecting dust can be discharged through bins without disturbances which will cause reentrainment of the dust with the gas stream.

The relatively wide central portion of each strip is, as has been noted, generally flat and may be provided with longitudinally extending stiffening beads, corrugations or channels. The entire electrode strip, moreover, is of constant wall thickness and the electrode strip is symmetrical in a plane parallel to the longitudinal edges of the strip and through the center thereof. The

beads or troughs formed in the flat central portion may likewise be of generally trapezoidal cross-section and the entire arrangement is designed so that the trapezoidal edge chambers and the stiffening channels open at one face of the electrode strip while the ridges or crests associated with the trapezoidal chambers and of the channels project from the opposite face of the strip. The result is a collector electrode having excellent utilization of material which can be stacked easily and shipped utilizing only a small space and which can be oriented with respect to the adjacent electrode strips such that the adjoining strips are rotated through 180 with respect to one another. In other words each electrode appears as if it had been rotated through 180 about the axis formed by the intersections of the symmetry plane and the central-portion plane, relative to the adjoining electrodes. The trapezoidal chambers moreover have been found to increase the collecting power of the individual electrodes.

According to a further feature of the invention, the electrodes are secured in the conventional manner to an upper carrying structure and at the lower ends are securely bolted, welded or riveted to a guide which serves also as a rapping rod. This manner of connection insures effective transmission of the vibrational energy which is applied by the rap to the individual strips.

' of riveting or tack welding for joining adjacent collector electrode strips reduces the cost of manufacture and the danger of transverse flow being eliminated, there is no disturbance of collection of the dust upon rapping.

5. DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 isa transverse cross-sectional viewthrough a collector electrode strip according to the present invention;

FIG. 2 is a transverse cross-sectional view, partly in diagrammatic form, showing the relationship of two collector electrode arrays with other elements of an electrostatic precipitator;

FIG. 3 is a fragmentary elevational view of the lower edge of the array; and

FIG. 4 is a detail view illustrating the labyrinth seal according to the present invention.

6. SPECIFIC DESCRIPTION Each collector-electrode strip 1 comprises a. flat central portion 2 lying generally along an electrode plane P which is perpendicualr to a transverse plane of symmetry P which intersects the plane P at an axis A. Along the edges portions of the strip, which should occupy in total no more than 5 to 10 percent of the transverse width, I provide trapezoidal profiles 4, each of which defines within the interior of its channel, a receiving chamber 4.

The free leg (outer leg) 5 of each trapezoid has a laterally and outwardly bent flange 6 which, as can be seen in'FIG; 4, overlaps the leg of an adjoining strip to define an air gap 7 which constitutes a labyrinth seal.

Assume a gas flow over the face of the left-hand electrode strip in FIG. 4 as indicated by the arrows B. As the gas passes over the crest 4" of each trapezoidal edge, there is little tendency for any inward deflection of the gas as represented by the arrow C and a transverse flow does not, therefore, occur from this side of the plates to the other. As far as the flow lines D of the gas on the other side of the plates are concerned, any transverse flow would require deflection in several directions and is excluded as represented by the arrow E.

Reverting to FIG. 1, it can be seen that the central portion 2 of the electrode strip is provided at spacedapart locations with longitudinally extending parallel heads 3, here shown to be formed by the corrugations, recesses or troughs deformed from the sheet material so that the entire strip is of constant wall thickness 2. The depth d of recess 3 or trough (which is of trapezoidal configuration) is generally equal to l to 1.5 mm or greater and is approximately equal to 2 or 3 times the thickness of the electrode strip while the transverse width w of the channel 3 may be appropriately 7 to 20 times the thickness t. The depth S of each collecting or receiving chamber 4', however, may range between l5: and 25: while the width W of the chamber at its maximum is likewise between 5: and 20!. The leg 5 extends to a distance s between 2! and beyond the plane P and is formed with the flange or foot which may have a width p of 2! to The foot or flange 6 includes an angle y between 75 and 105, preferably 90, with the leg 5 which, in turn, lies at an obtuse angle B of approximately 95 to 120, preferably about 105, to the plane P. The angle a between this plane and the inner limb of the trapezoid 4 may likewise range between 95 and 120 and is preferably about 105. The beads 3 may be spaced apart by distances L of to 90: and a similar distance may be provided at L between each of the outermost beads and the chambers 4.

Referring now to FIG. 2, in which an electrostatic precipitator is shown in diagrammatic form, it will be apparent that the adjoining plates 1 are rotated relative to one another about the axis A through 180 and thus form arrays of plates as represented at 10 and 11, respectively. Two arrays of plates form a channel 12 through which dust-laden air is induced to flow as represented by the blower l3. Corona-discharge electrodes 14 may be located in the space between the arrays of electrode strips and a jolting arrangement may be provided as represented by the motor 15 and hammer 16 and the rapping rod or anvil 17. A high-voltage source is connected to the electrode systems as represented at 18. A rapper 19 has also been illustrated in FIG. 3 to engage the guide or rapping rod shown at 20. Rivets 21 attach the lower edges of the strips 1 to this rod. The rapping devices of FIGS. 2 and 3, the blower of FIG. 2 and the electrostatic precipitator housing H thereof have been illustrated diagrammatically, but it should be noted that such structures are conventional in the art and that any convention arrangement for the specified functions may be used with the novel electrode system of the present invention. A specific electrostatic dust collector with a rapping arrangement for the collecting electrode is disclosed, for example, in MARKS MECHANICAL ENGINEERS HAND- BOOK, McGraw-Hill Book Co., N.Y., 1958, Chapter 9, pages 17 ff and Chapter 7, pages 61 ff.

I claim:

1. An electrostatic precipitator comprising an array of corona-discharge electrodes, a pair of spacedly juxtaposed collector electrodes flanking said coronadischarge electrode, and rapping means for jolting said collector electrodes, each of said collector electrodes comprising a plurality of substantially identical sheetmetal strips disposed generally along a common plane in substantially adjacent but spaced-apart relation, said rapping means including a rap bar common to all of the strips of a respective collector electrode disposed along a common plane and secured to said strips, said strips being of a uniform wall thickness of substantially 1 to 1.5 mm and each comprising a generally flat central portion lying in the respective plane and stiffened with longitudinally extending transversely spaced parallel beads projecting along one face of the strip and forming troughs open along the opposite face thereof, and respective longitudinal edge portions having generally the cross-sectional configuration of a trapezoid open at its broad base flanking said central portion, each of said edge portions including a first limb defining a leg of the trapezoid including an obtuse angle with the respective central portion and extending away from its plane to a distance greater than the height of said beads, a second limb on an end of said first limb and extending parallel to the respective plane away from the respective central portion while forming the small base of the trapezoid, a third limb connected to said second limb and including an obtuse angle therewith while extending from said second limb beyond the respective plane and forming the second leg of the trapezoid, and a flange bent at substantially a right angle to said third limb away from the respective central portion, the edge portions of adjacent strips of each collector electrode defining an air gap between them, the flanges of adjacent strips extending into said air gap and mutually overlapping the said air gap in substantially mutually parallel relationship to restrict crossflow between opposite sides of the collector electrodes.

2. The electrostatic precipitator defined in claim 1 wherein said strips have a wall thickness t, a depth d of said troughs equal to substantially 2t to 31 inclusive, said troughs having a transverse width w equal to substantially 71 to 20! and being of trapezoidal configuration, said edge portions having a trapezoidal altitude S between substantially 151 and 251 and a width w at its open side ranging substantially between 5 t and 20:, said third limb extending beyond said plane through a distance s between substantially 2t and 10!, said flange having a width p between substantially 2t and 15!, said first limb including an angle a between substantially 95 and 120 with said central portion, said third limb including an angle B with said second limb between substantially 95 and 120, said beads being spaced apart by a distance L of 30t to t, said edge portions each being spaced by a distance L from the nearest bead of the central portion between substantially 30: and 901.

3. A collector electrode for an electrostatic precipitator, comprising at least two substantially adjacent but spaced-apart sheet-metal strips, each of said strips including a generally flat central portion lying in a plane of said electrode and provided along its edges with respective longitudinal edge portions having generally the cross-sectional configuration of a trapezoid open at its broad base, each of said edge portions including a first limb defining a leg of the trapezoid including an obtuse angle with the respective central portion ranging between substantially and a second limb on an end of said first limb and extending parallel to the planeof the respective central portion while forming the small base of the trapezoid, a third limb connected to said second limb and including an obtuse angle therewith of substantially 95 to 120 while extending from said second limb beyond said plane and forming the second leg of the trapezoid, and a flange bent at substantially a right angleto said third limb away from the respective central portion, the edge portions of said adjacent strips of each collector electrode defining an airgap between them, the flanges of adjacent strips extending into said airgap and mutually overlapping at said airgap in substantially mutually parallel relationship to restrict crossflow between opposite sides of the collector electrode. 

1. An electrostatic precipitator comprising an array of coronadischarge electrodes, a pair of spacedly juxtaposed collector electrodes flanking said corona-discharge electrode, and rapping means for jolting said collector electrodes, each of said collector electrodes comprising a plurality of substantially identical sheet-metal strips disposed generally along a common plane in substantially adjacent but spaced-apart relation, said rapping means including a rap bar common to all of the strips of a respective collector electrode disposed along a common plane and secured to said strips, said strips being of a uniform wall thickness of substantially 1 to 1.5 mm and each comprising a generally flat central portion lying in the respective plane and stiffened with longitudinally extending transversely spaced parallel beads projecting along one face of the strip and forming troughs open along the opposite face thereof, and respective longitudinal edge portions having generally the cross-sectional configuration of a trapezoid open at its broad base flanking said central portion, each of said edge portions including a first limb defining a leg of the trapezoid including an obtuse angle with the respective central portion and extending away from its plane to a distance greater than the height of said beads, a second limb on an end of said first limb and extending parallel to the respective plane away from the respective central portion while forming the small base of the trapezoid, a third limb connected to said second limb and including an obtuse angle therewith while extending from said second limb beyond the respective plane and forming the second leg of the trapezoid, and a flange bent at substantially a right angle to said third limb away from the respective central portion, the edge portions of adjacent strips of each collector electrode defining an air gap between them, the flanges of adjacent strips extending into said air gap and mutually overlapping the said air gap in substantially mutually parallel relationship to restrict crossflow between opposite sides of the collector electrodes.
 2. The electrostatic precipitator defined in claim 1 wherein said strips have a wall thickness t, a depth d of said troughs equal to substantially 2t to 3t inclusive, said troughs having a transverse width w equal to substantially 7t to 20t and being of trapezoidal configuration, said edge portions having a trapezoidal altitude S between substantially 15t and 25t and a width w at its open side ranging substantially between 5t and 20t, said third limb extending beyond said plane through a dis-tance s between substantially 2t and 10t, said flange having a width p between substantially 2t and 15t, said first limb including an angle Alpha between substantially 95* and 120* with said central portion, said third limb including an angle Beta with said second limb between substantially 95* and 120*, said beads being spaced apart by a distance L of 30t to 90t, said edge portions each being spaced by a distance L'' from the nearest bead of the central portion between substantially 30t and 90t.
 3. A collector electrode for an electrostatic precipitator, comprising at least two substantially adjacent but spaced-apart sheet-metal strips, each of said strips including a generally flat central portion lying in a plane of said electrode and provided along its edges with respective longitudinal edge portions having generally the cross-sectional configuration of a trapezoid open at its broad base, each of said edge portions including a first limb defining a leg of the trapezoid including an obtuse angle with the respective central portion ranging between substantially 95* and 120*, a second limb on an end of said first limb and extending parallel to the plane of the respective central portion while forming the small base of the trapezoid, a third limb connected to said second limb and including an obtuse angle therewith of substantially 95* to 120* while extending from said second limb beyond said plane and forming the second leg of the trapezoid, and a flange bent at substantially a right angle to said third limb away from the respective central portion, the edge portions of said adjacent strips of each collector electrode defining an airgap between them, the flanges of adjacent strips extending into said airgap and mutually overlapping at said airgap in substantially mutually parallel relationship to restrict crossflow between opposite sides of the collector electrode. 